Sputtering and other types of physical vapor deposition (PVD) are commonly used in the semiconductor manufacturing industry to deposit films on substrates. PVD is a deposition process that takes place in the gas phase in which a source material is physically transferred to a substrate in a vacuum. PVD includes thermal and e-beam evaporation in addition to sputtering. PVD is commonly used to deposit metals, barrier materials and oxides. The source material is typically present in a target which acts as a cathode in the deposition operation.
In sputtering cathodes, the source material provided in the form of a target is eroded by energetic ions from a plasma discharge and the material liberated by the ions deposits as a thin film on the substrate via physical vapor deposition, PVD. The plasma discharge is generally maintained in an evacuated process chamber, i.e., a vacuum chamber, under controlled flow of a working gas with an electric potential and discharge current applied by a power supply between the target cathode and an anode.
In the case of electrically conductive target materials, the target may be supplied with a continuous or pulsating negative voltage, such that a plasma forms above the target surface. By means of an electrical field formed between the plasma and target surface, positively charged ions from the plasma are accelerated toward and onto the negatively biased target surface, i.e., the cathode, bombarding the target surface and causing erosion of the target by freeing materials from the target and resulting in material being sputtered away from the target surface. The liberated material from the eroding target is directed to a substrate such as a semiconductor substrate or other workpiece positioned in the deposition chamber.
In magnetron sputtering systems, the plasma density above the target is strongly increased by means of magnetic fields. Ions in the high plasma density region produced by the magnetic field, become highly energized. The magnetic fields are produced by a magnet arranged in close proximity to the target. The magnet is typically disposed on the side of the target opposite the target sputtering surface, i.e. behind the target.
In conventional magnetron sputtering systems, however, the target will have an uneven erosion profile. Regardless of its shape, the target erodes more preferentially at specific locations with respect to the fixed magnetic fields of the magnet. The uneven erosion profile of the target may result in poor uniformity of the deposited film and uneven film characteristics across the substrate. For example, poor step coverage may be achieved at some spatial locations of the substrate while good step coverage may be achieved at other areas of the substrate.
In today's rapidly advancing semiconductor manufacturing industry and with semiconductor devices having increasingly miniaturized features, it has become increasingly important to overcome the shortcomings of the art and provide deposited thin films with superior uniformity and consistent qualities.